As Mr Pomeroy remonstrated, Pencille swung the knife and plunged it into his neck, jurors were told.

Chelsea Mitchell, 27, is accused of assisting Pencille by helping him change his appearance as he fled from the train minutes after the attack.

Mr Hallam said: ‘Eyewitnesses saw what they thought was the two men trading punches. They were half right.

‘They saw Lee Pomeroy punching the first defendant, defending himself, having been stabbed in the neck by him. But the first defendant wasn’t punching back, he was stabbing. Again, and again, and again.

‘The 18 knife wounds found to Lee Pomeroy’s body when it was examined in a post-mortem provided the dreadful proof of the savagery of the first defendant’s unrelenting assault upon him – with a wound to his neck, eight to his torso, and others to his arm, his hands and his thigh, all inflicted in a matter of seconds in the same sustained attack.’

The court heard the train reached Clandon station at 1.06pm and Pencille gathered his belongings before fleeing.

He allegedly dumped his hat, sunglasses and jacket in woodland before meeting Mitchell.

Mr Hallam said: ‘Minutes after he killed a man he's talking to her and it's obvious what the two of them would have spoken about, what was at the forefront of his mind. He's killed somebody - what to do and how he needs her help.’